Design and Analysis of Leak-Testing Methodology for Gas Lift Valves

Abstract

Summary Properly operating gas lift valves (GLVs) allow annular gas to flow into the tubing and prevent any backflow. However, erosion, corrosion, and other effects may cause a GLV to leak, thereby posing a serious safety issue. Suspected leaking GLVs are often retrieved for inspection to address safety issues. Proactive testing is a way to minimize costly interventions. Accordingly, nonintrusive test procedures have emerged. For example, tests entailing monitoring of annular transient-pressure response can establish a GLV's integrity by avoiding valve retrieval for inspection. This study details the development of a forward model that helps design methodology for GLV testing. The model recommends drawing down the annular gas to develop a positive pressure differential to allow fluid flow from the tubing into the annulus through the suspected GLV. This drawdown (DD) is followed by a pressure-buildup (BU) test. These pressure-transient tests allow the determination of the integrity and extent of GLV damage. The forward model also allows the estimation of the time needed for each segment of the transient-test sequence, thereby helping to schedule such tests at a certain operational frequency.